title: Reliability and validity of the short questionnaire to assess health-enhancing physical activity (SQUASH) in patients after total hip arthroplasty.
abstract: BACKGROUND
  Despite recognized benefits of regular physical activity on musculoskeletal fitness as well as general health, little is known about the physical activity behavior of patients after Total Hip Arthroplasty (THA). So far, no physical activity questionnaire has been validated in this category of patients. As the Short Questionnaire to Assess Health-enhancing physical activity (SQUASH) has been shown to be a fairly reliable and valid tool to gauge the physical activity behavior of the general Dutch adult population, we measured the reliability and relative validity of this tool in patients after THA.
  
  
  METHODS
  44 patients (17 men and 27 women, mean age 71 +/- 8 years) completed the SQUASH twice with an in-between period of 2 to 6 weeks (mean 3.7). Reliability was determined by calculating the Spearman correlation coefficient between the activity scores of the separate questions as well as the total activity scores from both administrations. Additionally, a Bland & Altman analysis was performed for the total activity scores. Relative validity was determined using the Actigraphaccelerometer, worn by 39 patients (15 men and 24 women, mean age 70 +/- 8 years) for a 2-week period following the second questionnaire, as a criterion measure.
  
  
  RESULTS
  Spearman's correlation coefficient for overall reliability was 0.57. It varied between 0.45 and 0.90 for the separate questions. No systematic biases between readings were found. The Spearman correlation between Actigraph readings and total activity score was 0.67. It was 0.56 for total minutes of activity, 0.20 for time spent in light intensity activity, 0.40 for moderate activity and 0.35 for vigorous activity. Systematic bias was found between the SQUASH and the Actigraph.
  
  
  CONCLUSIONS
  The SQUASH can be considered to be a fairly reliable tool to assess the physical activity behavior of patients after THA. Validity was found to be comparable with those of other questionnaires, and as it is short and easy to fill in, it may prove to be a useful tool to assess physical activity in this particular subset of the population. However, the considerable systematic bias found in this study illustrates the need for further analysis of the validity of the SQUASH.
authors.affiliation: Department of orthopedics, university medical center Groningen, university of Groningen, the Netherlands. r.wagenmakers@orth.umcg.nl
authors.forename: Robert
authors.initials: R
authors.lastname: Wagenmakers
authors.forename: Inge
authors.initials: I
authors.lastname: van den Akker-Scheek
authors.forename: Johan W
authors.initials: JW
authors.lastname: Groothoff
authors.forename: Wiebren
authors.initials: W
authors.lastname: Zijlstra
authors.forename: Sjoerd K
authors.initials: SK
authors.lastname: Bulstra
authors.forename: Johan W J
authors.initials: JW
authors.lastname: Kootstra
authors.forename: G C Wanda
authors.initials: GC
authors.lastname: Wendel-Vos
authors.forename: Jos J A M
authors.initials: JJ
authors.lastname: van Raaij
authors.forename: Martin
authors.initials: M
authors.lastname: Stevens
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000592:standards* / Q000639:trends; D015331:Cohort Studies; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology; D011446:Prospective Studies; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards*